1. Field of the Invention
The present invention relates generally to multimedia transmission systems and more particularly to systems and methods for transmitting high definition digital video and standard definition analog video over a single cable.
2. Description of Related Art
With the advent of digital broadcast television and streaming video technologies various video cameras, monitors and video recorders have become available with enhanced resolution and advanced features. Closed circuit television (“CCTV”) systems now offer high definition video outputs and compressed digital video signals for use in applications such as premises surveillance, access control and remote monitoring of facilities. However, legacy systems remain in place and standard definition analog video signals are in widespread use and will continue to be used during the transition to all-digital, high-definition systems. In particular, coaxial cable (“Coax”) has been deployed to carry signals from CCTV cameras to monitoring stations. Some deployed CCTV cameras transmit compressed video signals over local area networks, or wide area networks, and these cameras may use the Internet Protocol (“IP”) as a communications means for transmitting the compressed video signal.
FIG. 1 illustrates conventional systems using Coax to carry standard definition analog video. A basic analog camera 10 typically generates a composite video baseband signal (“CVBS”) that can be transmitted up to 300 meters using Coax 11. The CVBS signal is commonly provided to a video recording system which often comprises a digital video recorder (“DVR”) 12 that records the CVBS in digital format. A conventional monitor 14 may be connected to the DVR 12 to simultaneously display the standard definition analog video, which generally has a resolution of 720×480 pixels.
Digital camera 16 may supplant analog camera 10 in some applications. The digital camera 16 may support a serial digital interface (“SDI”) that can be used to transmit uncompressed standard definition digital video over Coax 17 to DVR 12 at approximately 270 Mbps.
FIG. 2 illustrates conventional approaches to transmitting high definition video (1920×1080 pixels) in currently deployed systems. First, a digital camera 20 may support a high-definition serial digital interface (HD-SDI) that can be used to transmit uncompressed high-definition digital video over Coax 21 to DVR 22 at the rate of 1.5 Gbps. The cable distance supported under such high transmission rate is up to 100 meters. Second, an IP-based, high-definition (“HD”) camera 24 may generate a compressed digital HD video signal over 100 Mbps Ethernet using standard category 5 (“CAT5”) twisted pair cable 25 for distances up to 100 meters. The signal is received by a DVR 22 and recorded for non-real time playback. Existing Coax 26 can be used to transmit video from camera 24 to a DVR 22 using CAT5-to-Coax bridge modems 27 and 29 or other conversion devices. The use of networking to enable the camera to transmit digital video allows these systems to add some upstream communications, typically control and audio signals 28.